1. Field of the Invention
The present invention relates to a structure of and a manufacturing method for a semiconductor device and, more particularly, to a structure of and a manufacturing method for a device which employs a ferroelectric substance and is ideally used for a memory.
2. Description of Related Art
Name of Literature: Appl. Phys. Lett., Vol. 69, p.p.3188-3190 (1996) by Keiko Kushida-Abdelghafar, Hiroshi Miki, Kazuyoshi Torii, and Yoshihisa Fujisaki.
In a current manufacturing process of a semiconductor device, a step for performing heat treatment in a H2 gas is essential. The step for carrying out the heat treatment in the H2 gas has been extensively implemented as an important step for stabilizing characteristics of a device, typically represented by a MOSFET, thereby improving reliability.
As a ferroelectric substance, Pb(ZrxTi1-x)O3 (hereinafter referred to as xe2x80x9cPZTxe2x80x9d) is being considered to be applied to a memory or a storage cell, more particularly to a ferroelectric memory. A capacitor part of a ferroelectric memory employing PZT generally employs Pt as an electrode. As shown in the above literature, in a Pt/PZT/Pt multilayer structure, a film quality of a PZT layer is changed by the heat treatment in the H2 gas. The change causes degradation of a hysteresis characteristic of the ferroelectric capacitor.
In addition to the PZT mentioned above, many other materials are being zealously studied as candidate ferroelectric or high-dielectric-constant materials applicable to semiconductor devices. Such ferroelectric materials include SrBi2Ta2O9 (SBT), Pb5Ge3O11, Bi4Ti3O12, and BaxSr1-xTiO3. Such high-dielectric-constant materials include Ta2O5, ZrO2, HfO2, and CeO2.
The above materials are characterized in that they are all oxides. The foregoing PZT and oxides present a problem in that the heat treatment in a reducing atmosphere, such as in the H2 gas, causes oxygen to be eliminated due to a reductive reaction, and compositions of the oxide materials are changed.
For example, in the case of the ferroelectric memory employing PZT, the heat treatment in the H2 gas mentioned above changes the film quality, deteriorating the characteristics, especially the hysteresis characteristic, of the memory. On the other hand, skipping the heat treatment in the H2 gas poses a problem of unstable characteristics of other devices, including transistors.
Thus, there has been a problem in that the conventional manufacturing process cannot be used as it is when applying the aforesaid materials to the ferroelectric memories or the like.
Accordingly, an object of the present invention is to provide a structure of a semiconductor device that obviates the need for heat treatment in a hydrogen atmosphere after completion of a semiconductor manufacturing process. It is another object of the present invention to provide a manufacturing method for a semiconductor device whereby degradation of a hysteresis characteristic of a ferroelectric memory or the like can be prevented.
To these ends, according to one aspect of the present invention, there is provided a structure of a semiconductor device, including: a MOS transistor on a substrate; and a hydrogen occluding material used for wiring is disposed via an interlayer dielectric in the vicinity of a top of the MOS transistor. The hydrogen occluding material is subjected to heat treatment in an atmosphere containing hydrogen thereby to occlude hydrogen. Thereafter, heat treatment is performed in an atmosphere that contains no hydrogen so as to make the hydrogen occluded by the hydrogen occluding material be released. This causes hydrogen to be supplied to the MOS transistor and other devices formed on the substrate to stabilize the characteristics thereof.
According to another aspect of the present invention, there is provided a manufacturing method for a semiconductor device including the steps of: forming a MOS transistor on a substrate; forming a hydrogen occluding compound, more specifically, a hydrogen occluding silicide, on a source-drain and gate electrodes of the MOS transistor; and subjecting the hydrogen occluding silicide to heat treatment for occluding hydrogen in an atmosphere containing hydrogen. The silicide consists of one metal selected from among Ta, Ti, Zr, Fe, Cr, La, and Th, and Si. Heat treatment is performed in an atmosphere free of hydrogen in a subsequent step to release hydrogen from the silicide that has occluded hydrogen so as to supply hydrogen to the MOS transistor and other devices, thus enabling the characteristics thereof to be stabilize. Thus, the objects described above can be fulfilled.